Colds try to be benign, for humans that means nice thick mucus that is easy to cough up, for bats that hang upside down thin watery mucus that drains easily is best, thin watery mucus in a human is hard to get out if you are upright or on your back, resting on your side and alternating sides is best and lets each lung drain.
https://www.xopt1.com/blog/postural-drainage-techniques-home/